Catheter apparatus

ABSTRACT

A catheter having walls of which at least a portion is electrically conductive and has an electrical resistivity approximately equal to the electrical resistivity of blood.

1 United States Pat ent Kahn et al. [4 1 May 2, 1972 54] CATHETERAPPARATUS 3,473,087 10/1969 Slade ..317/2 R 3 166,688 1/1965 Rowand etal. ..317/2 R 72 Inventors. Alan R. Kuhn, Morrest wn, Florence A. 1 8mm.Maple Shade a of Ni 3,428,046 2/1969 Remer et al ..128/349 R [73]Assignee: Medtronic, Inc., Minneapolis, Minn. F REIGN PATENTS ORAPPLICATIONS [22] Filed: Apr. 8, 1970 1,033,971 6/1966 Great Britain..128/348 Appl' 26697 Primary Examiner-Dalton L. Truluck Attorney-LewSchwartz and Donald R. Stone [52] US. Cl ..l28/2 R, l28/2.05 R, 128/348,

138/118, 317/2 R [57] ABSTRACT [51] Int. Cl ..A6lb 05/02, A61m 25/00 58Field of Search ..128/2.05 R, 2.05 D, 2.06 R, A catheter having walls ofwhich at least a Portion is electril28/2.06 E, 2, 348-351; 138/1 18;317/2 R cally conductive and has an electrical resistivity approximatelyequal to the electrical resistivity of blood. [56] References Cited 7Claims, 5 Drawing Figures UNITED STATES PATENTS Sheridan ..128/348 XPatented May 2, 1972 m m V m ALAN 2 K411,

izaezwcz' A 6720x821 CATHETER APPARATUS BACKGROUND OF THE INVENTION Thisinvention is concerned with an improved catheter. Catheters constructedas hollow tubes are well known in the art for their use in the practiceof medicine as well as in medical research. Catheters are used, forexample, to measure pressures in body organs and in the circulatorysystem, to withdraw samples of body fluids, and to introduce drugs,intravenous fluids, X-ray contrast media, dyes for cardiac outputmeasurements, and nasogastric feeding.

In performing functions such as those mentioned above, the catheter ortube is normally filled with solutions which are electricallyconductive. In many of these applications, one end of the catheterterminates inside the body in close proximity to the heart while theother end is attached to an electrical device or electronicinstrumentation. As the catheter is normally made of an electricallyinsulating material, the solution within the catheter acts as anisolated circuit for electrical current into the body, and closeproximity to the heart causes the possibility of accidental death due toaccidentally applied electrical power which will be felt near the heartand may cause ventricular fibrillation.

The above-mentioned danger is now well known to those skilled in theart, and various studies are being conducted to overcome the problem.The apparatus of the present invention does overcome the problem byproviding a catheter having a conductive wall so that electrical currentis disbursed through the blood and body tissues rather than beingconcentrated at or near the heart.

SUMMARY OF THE INVENTION Briefly described, the apparatus of thisinvention comprises a tube having walls at least a portion of which iselectrically conductive or semiconductive material and has an electricalresistivity sufficient to prevent harmful current flow to organs withinthe body when the tube is used as a catheter for intracorporealapplications.

IN THE DRAWINGS FIG. 1a is a representation of the catheter apparatus ofthis invention;

FIG. 1b is a representation of the apparatus of this'invention as it isin the process of being assembled;

FIG. 2 is a schematicized drawing representative of the current densitypattern in the body of a human being between a pair of skin electrodes;

FIG. 3 is a schematicized drawing of the current density pattern betweena prior art intravascular catheter anda skin electrode; and

FIG. 4 is a schematicized diagram of the current density pattern betweenan intravascular catheter of this invention and a skin electrode.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT Resistance (ohms) Xarea(cm?) which equations is knownto those skilled in theart.

Referring to FIG. la, it should 'be' understood that thecatheter-apparatusof this invention comprises ahollow tube Rho (ohm-em.)

or catheter with electrically conductive or'semiconductive wallsl4-which have electrical resistivity. The catheter apparatus must bedurable and preferably flexible. In FIG. lb,

there is shown in the stage of construction a catheter of this invention10 which is being made by winding a base material 11, such as a Dacronmesh, around a rod 12, preferably a stainless steel rod.

The apparatus of this invention has been made by first coating rod 12with wax and then cutting a base material 11, such as Dacron or nylonmesh, into 3-foot long strips, 1 centimeter wide. Mesh 11 is then woundon rod 12 in a helical pattern with overlapping windings. A solution isthen applied to the base material 11 in sufficient quantities to flowthrough the base material, the solution being one which will harden intoa durable, flexible, electrically conductive or semiconductive coatingwhen cured. The solution is then cured, and when dry, further coatingsare applied and dried as necessary to form walls 14. A solution whichhas been used in the preferred embodiment of the apparatus of thisinvention is a flexible carbon impregnated elastomer, known as EccocoatNo. 258, which has a measured volume resistivity of about 133.5 ohm-cm.This material wasthinned out with a solvent and painted on the basematerial 11, using enough solvent to cause the material to flow throughmesh 11. It was than dried in a 150 F. oven for 15 minutes. A secondcoat was then painted on using a thicker solution of the material thanin the previous step, and it was again dried in the oven. Two furthercoats of the material were added as in the latter step. The completedcatheter was then removed from rod 12. This catheter, comprising theapparatus of this invention, was tested in a manner to be more fullydescribed below. Other materials which could be used to fabricate theapparatus of this invention include carbon-filled polyethylene,carbon-filled polyvinylchloride, carbon-filled rubber, and carbon-filledsilicones. Catheters can also be fabricated from such materials alonewithout the need for the mesh base as described previously.

To best understand the operation of the apparatus of this invention,reference should be made to FIGS. 2, 3, and 4 of the drawings.

As stated above, electrical shock hazards resulting from defectivemedical electrical equipment are well known in the art. It is commonknowledge that cycle alternating current greater than 100 milliamperescan be dangerous when flowing through the human body between two pointson the body surface. The heart tissue is most susceptible'to suchcurrent, and electrocution deaths are most commonly the result ofventricular fibrillation of the heart.

Over the past decade, an increased awareness of the susceptibility ofthe heart to 60 cycle alternating electrical currents has beendeveloped. When a current flows between two points on the surface of thebody, it is distributed more or less unifomtly throughout the tissues,and the density of current at any single point deep inside the body iscomparatively small. This may be seen by reference to FIG. 2, where abody 15 has placed thereon a pair of electrodes 16 and 17 between whichis flowing a current indicated by current density lines 20. A review ofthe current density lines will indicate that when electrical currentflows through the body from two points on or near the body surface, thecurrent becomes distributed more or less uniformly in the body blood andtissues, and the current density at anyone point inside the body, suchas th heart, is relatively small.

The heart is highly sensitive to 60 cycle alternating current, andcurrents as low as 10 to 20 microamperes can cause fibrillation wheninjected over 1 square millimeter of heart muscle. However, to. generate10 microamperes per square millimeter of current density at the heartsurface from electrical contact on either arm, such as electrodes 16 and17 on body 15 of FIG. 2, it is necessary to provide a current flow ofmilliamvperes. This is because the current is effectively disbursedthrough-the volume of the blood and tissues in the body.

However, when a catheter containing electrically conductive liquid isintroduced near the heart, the current density situation issignificantlyaltered. In 'FIG. 3, there is again shown body 15 and electrode 16, butthe current density lines 21 nowiindicate theflow of current betweenelectrode 16 and an intravascular catheter 18 here shown to be a priorart hollow catheter having a nonconductive wall.

As can be seen in FIG. 3, catheter 18 terminates within the heart, andbecause of the conductive effect of the solution or liquid withincatheter l8, virtually all of the current passing through catheter 18exits at a small area near the heart muscle. That is, the currentdensity at the end of the catheter is sufficiently great so that aslittle as 20 microamperes of current can be lethal. Such small currentscan result from many accidental causes. For example, if the catheter isconnected to a grounded pressure transducer or fluid injector, as isoften the case, a small electrical potential introduced at any point onthe body can be dangerous. As a specific example, a nurse who may adjusta properly functioning bedlamp having an exposed metal part which is notgrounded can kill the patient by simply touching him.

It is, therefore, desirable that the walls of the catheter or at least aportion thereof be of a conductive material so that electrical currentsimpressed on the catheter may pass through the catheter walls into thebody and be disbursed to avoid density at the heart. If the walls of thecatheter are substantially better electrical conductors than thesurrounding blood and tissue, then the electrical current will pass outuniformly into the blood and tissue along the length of the catheter.However, if the catheter walls are highly conductive along its length aswell as through its walls, it will provide a low impedance between thesource of power and the heart and be even more dangerous than theabove-mentioned prior art catheter because very low voltages cangenerate high currents. Obviously then, a highly conductive catheter iseven more dangerous than a highly insulated catheter.

The catheter of the apparatus of this invention is selected to have aconductive or semiconductive surface with an electrical resistivityapproximately in the range from 12 to 1,200 ohm-centimeters, preferablyapproximately equal to the electrical resistivity of blood, 120ohm-centimeters. That is, the catheter apparatus of this invention has awall with at least a portion having an electrical resistivity ofone-tenth to times the electrical resistivity of blood.

Referring now to FIG. 4, there is again shown the body 15 and electrode16 and a plurality of current density lines 22 flowing between electrode16 and an intravascular catheter 10 comprised of the apparatus of thisinvention. In FIG. 4, it is apparent that the current begins to disburseat the site at which catheter 10 penetrates the skin of body 15. Thus,the pattern of dispersion is similar to that which would be present ifthe catheter 10 were not used and the current were injected from asurface electrode such as 17 in FIG. 2. It has been proven byexperimentation that greatly increased currents can be applied withoutcausing ventricular fibrillation of the heart when the apparatus of thisinvention, as shown in FIGS. 1a, 1b, and 4, is used in place of priorart catheters.

From the above, and with reference to FIG. 4, it will be apparent thatcatheter 10 need not be electrically conductive or semiconductive alongits entire length, but that it must include a part of its wall which isconductive or semiconductive at the point adapted to be in contact withthe skin after intracorporeal application of the improved catheter.

The improved catheter apparatus of this invention was built and testedin a live, intact dog under conditions normally present in human cardiaccatheterization. Similar tests were performed on a conventional catheternormally used in human diagnostic cardiac studies, in this case astandard No. 7 Lehman cardiac catheter.

A catheter of the apparatus of this invention was passed to the rightventricle of the heart through the femoral vein and wedged betweenmuscular trabeculations. The prior art catheter of identical length andintemal diameter was passed to the right ventricle through anotherfemoral vein and also wedged between muscular trabeculations. Sixtycycle AC current was applied to the catheter of this invention beginningwith 6 microamperes and increasing in 15 steps to 10,000 microamperes.Each current step was applied for 5 seconds.

Electrocardiogram and intraventricular pressures were monitoredcontinuously. No effect on the heart was observed. At the 10,000microamperes level, the animal's leg was seen to twitch where thecatheter entered the skin. Results of this test are shown in Table Ibelow.

The prior art catheter was then tested in a similar manner. However,when the current reached 70 microamperes, ventricular fibrillation ofthe heart occurred. The dog was restored immediately to normal sinusrhythm using DC cardioversion at 50 watt-seconds, in a manner known tothose skilled in the art. It is also interesting to note that at 50microamperes the dog began to have occasional ventricular prematurebeats. The results of this test are shown in Table II below. 1

TABLE II Prior Art Catheter Current-ua Time applied-sec. Response 6 5none l2 5 none 17.5 5 none 22 5 none 34 5 none 50 5 Doc. VPBS" 70 5Ventricular fibrillation (ventricular premature beats) The prior artcatheter was withdrawn to the vena cava, and the catheter of thisinvention was repositioned in the right ventricle. The above-describedtest was repeated, and again, no cardiac disturbances were observed.Again, the 10,000 microamperes current produced leg twitching. Referenceis made to Table III for the results of this test.

TABLE III Improved Catheter Apparatus Current-ua Time applied-sec.Response 6 5 none 23 5 none 5 none 240 5 none 740 5 none 1450 5 none3000 5 none 5 none 5 none 7 8000 5 none 10,000 5 leg muscle twitch Thecatheter of this invention was then withdrawn to the vena cava, and theprior art catheter was repositioned in the right ventricle. The abovetest was again repeated, and again, the dog had ventricular fibrillationof the heart at 70 microamperes of input current. Cardioversion againrestored normal sinus rhythm. The results of this test are shown inTable IV.

fibrillation The two sets of the last above two paragraphs were repeatedin sequence, with the same results. However, when using the prior artcatheter, the animal fibrillated at 50 microamperes but stopped afterthe current was turned ofi. When 70 microamperes was again reached,ventricular fibrillation occurred but was irreversible. The results ofthese further tests can be seen in Tables V and VI below.

TABLE V Improved Catheter Apparatus none I7 5 none 22 5 none 34 5 none50 5 Ventricular fibrillation (Stopped after current turned 06) 70. 5Ventricular fibrillation (Irreversible) From the above, it will beapparent that there is a great advantage in the use of a catheter havingat least a portion of its walls electrically conductive orsemiconductive and having an electrical resistivity which is comparableto that of the surrounding blood and tissues during an intracorporealapplication to allow current flow throilfigh the walls into the bloodand tissue, but to provide a sign [cant impedance between the source ofcurrent and the end of the inserted catheter. As explained above, thiselectrical resistivity lies approximately in the range of 12 to 1,200ohm-centimeters, and is preferably approximately at the electricalresistivity of the surrounding blood and tissue.

It will be apparent that construction of the catheter of this inventioncan be other than that described above with respect to the preferredembodiment. For example, rings or strips of conductive material may beembedded in an insulative materi- 7 al, a portion rather than all of thecatheter wall may be conductive, and in some cases only the portion ofthe catheter adapted to be adjacent to the skin during an intracorporealapplication may be conductive.

What is claimed is:

1. Catheter apparatus comprising tubular means having walls, at least aportion of said walls being electrically conductive and having anelectrical resistivity of approximately from 12 ohm-centimeters to 1,200ohm-centimeters.

2. The apparatus of claim 1 in which all of said walls are electricallyconductive and have an electrical resistivity of approximately from 12ohm-centimeters to 1,200 ohm-centimeters.

3. The apparatus of claim 1 in which the electrical resistivity of saidportion of said walls is approximately equal to the electricalresistivity of blood.

4. The apparatus of claim 3 in which the electrical resistivity of saidportion of said walls is approximately from one-tenth to 10 times theelectrical resistivity of blood.

5. The apparatus of claim 1 in which said portion of said wallscomprises a part of said walls adapted to be adjacent to the skin of ananimal during intracorporeal application of said catheter apparatus.

6. The apparatus of claim 1 in which said portion of said walls iselectrically semiconductive.

7. Improved catheter apparatus comprising: tubular means defining alumen for the passage of fluids into an animals body; and said meansbeing electrically semiconductive and having a substantially uniformelectrical resistivity selected in the range from approximately 12ohm-centimeters to 1,200 ohm-centimeters.

1. Catheter apparatus comprising tubular means having walls, at least aportion of said walls being electrically conductive and having anelectrical resistivity of approximately from 12 ohmcentimeters to 1,200ohm-centimeters.
 2. The apparatus of claim 1 in which all of said wallsare electrically conductive and have an electrical resistivity ofapproximately from 12 ohm-centimeters to 1,200 ohm-centimeters.
 3. Theapparatus of claim 1 in which the electrical resistivity of said portionof said walls is approximately equal to the electrical resistivity ofblood.
 4. The apparatus of Claim 3 in which the electrical resistivityof said portion of said walls is approximately from one-tenth to 10times the electrical resistivity of blood.
 5. The apparatus of claim 1in which said portion of said walls comprises a part of said wallsadapted to be adjacent to the skin of an animal during intracorporealapplication of said catheter apparatus.
 6. The apparatus of claim 1 inwhich said portion of said walls is electrically semiconductive. 7.Improved catheter apparatus comprising: tubular means defining a lumenfor the passage of fluids into an animal''s body; and said means beingelectrically semiconductive and having a substantially uniformelectrical resistivity selected in the range from approximately 12ohm-centimeters to 1,200 ohm-centimeters.